1. Field of the Invention
The present invention relates to a rotor having auxiliary permanent magnets of a rotary electric machine, particularly, an alternator for a vehicle.
2. Description of the Related Art
A rotor of an alternator for vehicle is, generally, composed of a field coil and a plurality of claw poles. Recently, in order to increase the output power, auxiliary permanent magnets are installed between the claw poles to increase the field magnetic flux.
For example, JP-A-8-223882 discloses a rotor structure of such an alternator. However, because the permanent magnets are fixed directly to the claw poles, it is difficult to hold the permanent magnets under a high rotation speed. In order to solve this problem, JP-A-7-123664 proposes another rotor structure which is provided with a resinous magnet holder. The resinous magnet holder is molded with the permanent magnets and held between the claw poles.
As the output power increases, temperature rise of the alternator becomes higher. Particularly, temperature of the claw pole surfaces becomes significantly high because of increased eddy current as field magnetic flux is increased. This requires a resinous magnetic holder made of heat resistant material, which is generally expensive. A metal magnetic holder is also expensive, because it must be made from non magnetic metal such as stainless steel.